Offline converters receive a voltage from an alternating current (AC) line and form a bulk voltage, which may then be converted into a different voltage for use by low-voltage circuitry. Typically a full-wave AC input voltage is converted into a half wave rectified voltage and smoothed before being converted into a lower voltage. One particularly useful feature for offline converters is power factor control. A power factor controller may be used in an offline converter to ensure that power is being efficiently delivered to a load with a high power factor by keeping the voltage and current waveforms in phase.
When operating, the power factor controller implements various voltage feed-forward and protection functions based on the level of the input voltage. For example, the power factor controller can sense a low line condition and adjust the on-time of a switch in response. The power factor controller can also detect a brownout condition in which it senses an abnormally low line for an extended time and take appropriate remedial actions. While these feed-forward and protection functions are useful, they use an integrated circuit terminal to sense the line voltage.
The use of the same reference symbols in different drawings indicates similar or identical items. Unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well.